The present invention relates to devices for removing obstructions from body lumens, and more particularly to catheters for removing atherosclerotic plaque and thrombotic occlusions from blood vessels.
Atherectomy catheters are known for their utility in removing atherosclerotic plaque and thrombotic occlusions from arteries. While intended mainly for use in the coronary arteries, such catheters may as well be used in peripheral vessels. Beyond coronary uses, such catheters can have neurological applications, e.g. removal of lesions in carotid arteries, gynecological use in recanalizing fallopian tubes, and a potential urological application for removal of benign prostate hyperplasia.
Atherectomy catheters have a variety of designs. According to one design, the catheter has a rounded or bullet shaped tip with an abrasive surface. At the treatment site, the tip is rotated at high speed and burrows through the occlusion. The resulting debris, typically in particulate form, is not captured by the device. Rather, it is allowed to flow to the capillary bed where it is absorbed. The device is most effective in abrading hardened (calcified) occlusions, with the intent being to produce particulate debris no larger than about 7 microns in diameter. When encountering softer occlusions, however, the device presents the risk of an occlusion breaking off during the atherectomy procedure, causing an acute and potentially life-threatening reclosure of the artery. The abrasive tip may inadvertently remove endothelium cells during catheter insertion, use or removal, thereby creating sites for potential lesions.
A second type of catheter employs a cartridge housed within the catheter, near the catheter distal tip. When the distal tip region is placed near the occlusion, plaque enters the cartridge through an opening or "cutting window". A cup-shaped blade then is rotated or oscillated at high speed, and advanced to cut and capture plaque that entered the cartridge. U.S. Pat. No. 5,312,425 (Evans); U.S. Pat. No. 5,087,265 (Summers); and U.S. Pat. No. 5,085,662 (Willard) disclose versions of atherectomy catheters with a movable blade or cartridge within a tissue collection volume near the catheter distal tip.
An example of an atherectomy catheter that depends on vaporization of plaque is found in U.S. Pat. No. 5,087,256 (Taylor). A dome-shaped head on the tip can be heated to temperatures in the range of 300-400 degrees C., for disintegrating plaque. U.S. Pat. No. 5,098,431 (Rydell) discloses a catheter in which an RF discharge between two spaced apart annular electrodes, electrosurgically cuts tissue to remove a blockage.
Conventional atherectomy catheters are limited principally to an axial cutting direction and subject to smooth cell muscle migration (restonosis) after treatment. Patients treated with conventional atherectomy devices have restonosis rates of 30-40 percent within the six months following treatment.
Therefore, it is an object of the present invention to provide an atherectomy catheter with a cutting edge that achieves a finer, more accurate cutting of unwanted tissue, to reduce the risk of acute blockage due to the breaking off of an occlusion.
Another object is to provide a tissue cutting element for an atherectomy catheter that is effective in severing calcified and soft occlusions.
A further object is to provide a flexible atherectomy catheter that incorporates means for capturing tissue being severed, to ensure against the escape of such tissue into the blood stream.
Yet another object is to provide an atherectomy catheter with enhanced versatility, due to the incorporation of longitudinal and transverse (arcuate) tissue cutting motions.
Further, it is an object of the present invention to provide an atherectomy catheter and procedure tending to seal the region of the cut, thus tending to reduce the incidence of restonosis.